1. Field of Invention
The present invention relates to a microwave antenna. More particularly, the present invention relates to a microstrip antenna which uses a dual-mode resonator to increase an operating bandwidth.
2. Description of Related Art
Telecommunication technologies have made dramatic progress owing to rapid technology advancement. There are also immense commercial opportunities for telecommunication providers. In wireless mobile telecommunication systems, the transmission and receiving of signals dominate the communication quality. It is, therefore, the primary objective to pursuit an antenna having a broad band and a high isotropic radiation field pattern. That is, increasing the operating bandwidth and making the radiation field pattern evenly distributed become the primary objective for designing an antenna.
Refer to FIG. 1, which shows a conventional portable antenna of a mobile phone. The mobile phone 14 includes a line antenna 10 and a spiral antenna 12. When the phone set is not in use, the line antenna 10 can be invaginated in the mobile phone 14. The spiral antenna 12 which has inferior radiation efficiency is responsible for receiving microwave signals at this time. When the phone set is in use, the line antenna 10 can then be pulled out to transmit or receive microwave signals with better radiation efficiency. This kind of portable mobile phone antenna is inconvenient to use though it improves the carrying problem of traditional line antennas.
Refer to FIG. 2, which shows another conventional portable mobile phone antenna. As shown in this figure, L-shape antenna 20 is constructed on the circuit board 22, which is positioned in the mobile phone case 24. This kind of built-in antenna will not affect the portability and operation of the users. It depends, however, on manual assembly, which will reduce the reliability for antenna duplication. Further more, though the antenna is directly grounded to reduce size, it also reduces the gain of the antenna.
Refer to FIG. 3, which shows a conventional toploaded antenna. The toploaded antenna is normally constructed on a case of a telecommunication transceiver. This will cause portability problems for personal mobile telecommunication equipment. In addition, the toploaded antenna which depends on manual assembly has disadvantages of poor reliability for duplication and high personnel costs during a manufacturing process of the telecommunication equipment.
Refer to FIG. 4, which shows a butterfly-shape plane antenna 41, which can be produced by using a printed circuit board. The butterfly-shape plane antenna 41 includes a butterfly-shape microstrip line 42 and a balun feed-in strip transmission line 44. The butterfly-shape microstrip line 42 and a balun feed-in strip transmission line 44 are built on both sides of the printed circuit board 40, respectively. For the butterfly-shape plane antenna 41 operating at center frequency of, for example, 1.7 GHz, the length of the rectangular loop of the balun feed-in strip transmission line 44 is about 1.7 cm. Taking into account of the balun feed-in strip transmission line 44, the size of the butterfly-shape plane antenna 41 is too large for a small-scale telecommunication transceiver.
Refer to FIG. 5, which shows a conventional dual-L plane antenna 50. As shown in the figure, the dual-L plane antenna 50 includes a grounded plane 52, a high-frequency resonator 54, and a low-frequency resonator 56, where the high-frequency resonator 54 and low-frequency resonator 56 are connected to the grounded plane 52 respectively. By changing the interval between these two resonators, the bandwidth of the antenna 50 can be adjusted. In practical application, however, the size of this antenna is still too big for mobile telecommunication equipment. Further more, there is a need of accurate metal working during the manufacturing process. Also, manual assembly produces larger error, which provides less accuracy during operations. Because the strength of the structure needs to be enhanced by copperizing the alloy to avoid shift and shaking, the manufacturing cost also increases due to the additional processes incurred.
Refer to FIG. 6, which shows a patch antenna. As shown in the figure, base board 60 includes patch resonators 62, 64, 66 on the same plane. The center frequency of the antenna is about 2.4 GHz. As shown in FIG. 7, the relative bandwidth of the antenna is about 1%.
As a summary from previous discussions, there are at least several defects for the microwave antenna structures mentioned:
1. Narrow operating bandwidth; PA1 2. Inconvenient to use because of the large size of the antenna; and PA1 3. Poor reliability and high personnel cost because of the manual assembly required.
In light of the foregoing, there is a need to provide a broad-band microstrip antenna for mobile telecommunication equipment.